Memory devices for storing and retrieving data are known in the art. For example, radio frequency ("RF") tags are available from a number of manufacturers, including Texas Instruments of Dallas, Tex. The manufacturing of wireless memory devices typically includes laminating a flexible circuit substrate carrying appropriate electrical and electronic devices, such as an RF tag, between a face sheet and a release liner to form a "smart label."
The flexible circuit substrate generally carries electrical connections such as traces and contacts on the surface of the substrate. In the case of an RF memory device, the flexible substrate also carries an antenna. The antenna typically takes the form of an electrical trace on the surface of the substrate. The flexible circuit substrate also carries an electronic structure, such as an integrated circuit. Coupling of the integrated circuit to the electrical traces or contacts typically employs flip-chip surface mounting techniques. Flip-chip mounting is a technique in which a leadless chip or die electrically and mechanically interconnects to the contacts by means of conductive bumps, such as solder, on the chip's face.
The integrated circuit typically includes a memory portion and a logic portion. The logic portion controls the reading, writing, or manipulating of data in the memory portion. The logic portion further couples the memory portion to the antenna to form a transmitter, receiver, or transceiver for reading or writing data to, or from, the RF tag. Thus, for example, an RF tag may receive and transmit RF signals to write data to the memory and to read data from the memory. In the case of a "passive" device, the chip may also include analog circuitry for deriving power from an RF field. Alternatively, a battery or other discrete power source may provide power to an "active" device.
The face sheet may provide a protective surface over a first surface of the circuit substrate, for example to protect the antenna and the electronic structure. The face sheet also provides a surface for carrying identifying indicia. A pressure sensitive adhesive may cover a second surface of the circuit substrate to readily affix the memory device to an item or container. The release liner provides a selectively removable protective layer over the pressure sensitive adhesive, that a user removes before applying the memory tag to an item or container.
The existing laminate structures and methods of manufacturing memory tags present certain problems. Current structures have been unable to take advantage of low cost chip-on-board surface mounting techniques such as wire bonding to couple the integrated circuit to the antenna, bonding pads, or contacts. This is in part due to the use of a flexible circuit substrate. Wire bonding techniques typically employ ultrasonic acoustic energy to bond the bonding wires to the bonding pads on the substrate. The flexible substrate tends to oscillate with the ultrasonic acoustic energy causing the bonding to fail. While stiff substrates, such as printed circuit boards formed of FR-4 are used for mounting integrated circuits, such stiff substrates are generally considered incompatible with the memory tag applications. For example, the face sheet tends to separate from the stiff substrate when a smart label is fed through a printer or when a continuous web of smart labels are rolled into a coil.
A further obstacle to the use of wire bonding in smart labels is the force asserted on the wire bonds during manufacturing and printing operations. For example, excessive stress and strain may be exerted on the bonding wires and the bonds by rollers in a device such as a printer or laminator. Such pressure will tend to break the bonding wires or cause the bonding wires to separate from the bonding pads. Such pressure may also cause damage to the integrated circuit.
A further drawback of existing structures is potential damage caused to a print head as it rides over discontinuities in memory devices. This is particularly a problem for thermal printers. Additionally, the discontinuity tends to lower print quality.